1. Field of the Invention
This invention relates to compressors and, more particularly, to an isothermal compressor apparatus and method for isothermally compressing a compressible gas.
2. The Prior Art
Compressors are well known in the art with their primary function being to increase the energy of a fluid and, more particularly, increase the pressure or compress a compressible gas. A typical compressor includes a reciprocating piston operating in a cylinder with valves controlling the movement of gas through the cylinder.
It is well known that compression of a compressible gas not only increases pressure but causes heating of the gas by the work of compression. The compressible gas is considerably hotter at the discharge than at the inlet. The gain in pressure imparted by a single-stage compressor is limited by the heating so that for high discharge pressures multistage compressors are required. The power required to compress a gas depends upon (1) the inlet temperature since compression of a hot gas requires more work than a cold gas and (2) the mechanical efficiency of the compressor which efficiency varies with the compression ratio. The compression ratio is defined as the ratio of the absolute discharge pressure to the absolute inlet pressure. Additionally, the absolute discharge pressure over the inlet pressure is proportional to the temperature of the discharge gas over the inlet temperature. To further understand the relationship of the temperature of a compressed gas with its pressure, the temperature of the compressed gas leaving a compressor cylinder (and before cooling) may be estimated from the expression for the adiabatic discharge temperature: EQU T.sub.b =T.sub.a (P.sub.b /P.sub.a)
Wherein Ta and T.sub.b are the absolute temperatures at suction and discharge, respectively, and Pa and P.sub.b are the inlet and discharge pressures, respectively. From the foregoing, it is clear that a substantial portion of the energy imparted to the compressible gas is in the form of thermal energy. This thermal energy has a direct effect on the pressure of the compressible gas and thereby interferes with the overall mechanical efficiency of the compressor. Additionally, unless captured by other means, this thermal energy is lost to the ambient thereby further lowering the overall energy efficiency of the compressor.
In view of the foregoing, it would be significant advancement in the art to provide an isothermal compressor apparatus and method whereby a compressible gas is isothermally compressed with the thermal energy imparted thereto being recovered and suitable utilized. It would also be an advancement in the art to provide an isothermal compressor apparatus whereby an evaporation chamber for removing thermal energy from the compressed gas is placed in close proximity to the compression chamber thereby providing more efficient transfer of the thermal energy from the compressed gas to a refrigerant in the evaporation chamber.